The exhaust system of a motor vehicle may comprise a catalytic converter with a lean NOx trap (LNT). The lean NOx trap has a multiplicity of ducts through which engine exhaust gases flow. During lean-burn operation of the engine, that is to say when a lambda value in the exhaust gas is greater than one, the lean NOx trap can collect nitrogen oxides (NOx) from the exhaust gas. Once the LNT has reached its storage capacity, it may begin to release NOx to the atmosphere. To prevent this, the LNT may be regenerated by converting the stored NOx via injection of a reactant, such as unburnt fuel, into the LNT.
The amount of nitrogen oxides stored in a lean NOx trap may be determined by a model of the lean NOx trap which takes into consideration the storage, the release and the conversion of the nitrogen oxides and the mass throughput of the nitrogen oxides upstream of the lean NOx trap. The rate of the NOx storage during lean-burn operation is dependent substantially on the spatial velocity, the temperature of the lean NOx trap and the normalized NOx storage level. The maximum storage capacity is dependent substantially on the size and design of the lean NOx trap and on the temperature of the catalytic converter. Said maximum storage capacity is then corrected for a deterioration in performance as a function of the thermal exposure over the lifetime of the lean NOx trap, also referred to as aging, and for the amount of stored sulfur, also referred to as poisoning.
However, the use of such models may be limited, as gradual changes to the storage capacity of the NOx trap may not be accounted for. Thus, the model may not be adapted in real time, leading to inaccuracies in the model.
The inventor has recognized the above issues and has provided a method herein to at least partly address the issues. A method for adapting a lean NOx trap (LNT) in an exhaust system of a motor vehicle is provided. The method comprises if a difference between an estimated NOx concentration and a measured NOx concentration in exhaust downstream of the LNT is greater than a threshold, calculating an adaptation value, the estimated NOx concentration downstream of the LNT based on a kinetic model, and adapting the kinetic model, adjusting one or more operating parameters of the LNT, and indicating an aging state of the LNT based on the adaptation value.
The disclosure provides an algorithm which is based on the NOx concentration downstream of the lean NOx trap and which provides a cascaded adaptation of the model. Said method permits real-time control using the NOx concentration downstream of the lean NOx trap. As a result of the cascading, that is to say the repeated relaying and use of the residual of the adaptation value, the latter is in a sense utilized multi-dimensionally, which permits particularly robust adaptation of the reaction.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.